Spark plug

ABSTRACT

A spark plug includes a central electrode member and an outer electrode member. The central electrode member includes a central base and a plurality of electrode prongs extending in an axial direction from the central base. The outer electrode member surrounds the central electrode member. The outer electrode member includes a wall that is radially spaced from the plurality of electrode prongs to allow a series of electric arcs to form between the wall and the plurality of electrode prongs. The outer electrode member and the central electrode member are sized and positioned relative to one another such that a first rate of wear of the outer electrode member, along a longitudinal axis of the spark plug, is substantially equal to a second rate of wear of the central electrode member along the longitudinal axis.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of United States patentapplication No. 17/304,637 titled “SPARK PLUG,” filed Jun. 23, 2021, theentire disclosure of which is expressly incorporated by referenceherein.

TECHNICAL FIELD

The present disclosure relates generally to a spark plug and, forexample, to a spark plug for a spark-ignition (SI) engine.

BACKGROUND

An internal combustion engine powers a machine by converting chemicalenergy stored in fuel (e.g., gasoline, compressed natural gas (CNG),methanol, ethanol, bioethanol, or another type of fuel) into mechanicalwork. In such an engine, air is mixed with the fuel to form an air- fuelmixture. Some engines utilize a spark plug, which typically includes acentral electrode and one or more outer electrodes. The spark plug maytransmit an electric current along the central electrode into a chamberthat is fluidly connected to or inside of a cylinder. A piston ismovably mounted within the cylinder to travel in a cycle between a topdead center (TDC) position and a bottom dead center (BDC) position. Insome embodiments, as the piston reaches the TDC position, a sparkresulting from the electric current jumps a gap between the centralelectrode and the one or more outer electrodes, causing the air-fuelmixture to combust. A force of the combustion drives the piston downtowards the BDC position, and the cycle repeats. Because the piston isconnected to a drivetrain of the machine, continued movement of thepiston propels and/or powers the machine.

While gaseous fuel (e.g., CNG, methanol, ethanol, bioethanol, and/or thelike) is known to provide a relatively low power density, such fuel isalso known to emit relatively low emissions. Thus, manufacturers havesought to produce engines that efficiently utilize such fuel. Forexample, to compensate for the relatively low power density provided bynatural gas, manufacturers have developed CNG engines that operate underhigh compression ratios. Because of the high compression ratios,however, the combustion of the air-fuel mixture exposes certain enginecomponents, such as a spark plug, to high temperatures and/orsignificant stress. As a result, the spark plug may be susceptible topremature wear, which may lead to increased costs associated withrepair, replacement, and/or machine downtime. Furthermore, in somecases, the electrodes may wear unevenly, leading to a widening of aspark gap between the electrodes which prevents the electric currentfrom bridging the spark gap. In such a case, in addition to theabove-described costs, valuable material may also be wasted.

U.S. Pat. No. 10,145,292 discloses a spark plug including a pre-chamberfor an engine. The spark plug includes a first cylindrical structurehaving a wall defining a bore. An electrode is positioned inside thebore such that the electrode is spaced apart from the wall to define atleast one electrode spark gap. The spark plug further includes a secondcylindrical structure configured to receive the first cylindricalstructure. The second cylindrical structure has one or more accessapertures configured to facilitate access to the wall of the firstcylindrical structure.

The spark plug of the present disclosure solves one or more of theproblems set forth above and/or other problems in the art.

SUMMARY

In some implementations, a spark plug includes a central electrodemember that includes a base and a plurality of electrode prongsextending from the base, wherein the base is substantially centered on alongitudinal axis that extends through a geometric center of a firstreference circle and a second reference circle, wherein the firstreference circle has a first diameter, and the second reference circlehas a second diameter that is greater than the first diameter by a gaplength, an electrode prong, of the plurality of electrode prongs,includes an axial portion and a radial portion, wherein the axialportion includes an outer surface that partially defines the firstreference circle, wherein the axial portion extends in an axialdirection that is substantially parallel to the longitudinal axis, andaxial portion has a width along a circumferential direction of the firstreference circle and a thickness along a radial direction that isperpendicular to the axial direction, and the radial portion connectsthe axial portion to the base; and an outer electrode member thatincludes an interior surface that defines the second reference circle,and wherein

$P = \frac{w^{2}\sqrt{l}}{t^{2.5}}$

where P is a parameter having a value in a range of approximately 1.5 toapproximately 7.5, w is the width in millimeters, l is the gap length inmillimeters, and t is the thickness in millimeters.

In some implementations, a spark plug includes a central electrodemember that includes: a central base, and six electrode prongs extendingradially and axially from the central base; and an outer electrodemember that is concentric with and surrounds the central electrodemember, wherein the outer electrode member includes a wall that isradially spaced from the six electrode prongs to allow a series ofelectric arcs to form between the wall and the six electrode prongs;wherein the outer electrode member and the central electrode member aresized and positioned relative to one another such that a first rate ofwear of the outer electrode member, along a longitudinal axis of thespark plug, is substantially equal to a second rate of wear of thecentral electrode member along the longitudinal axis.

In some implementations, a method includes activating a power systemthat includes a spark plug attached to a cylinder, the spark plugincluding: a central electrode member extending an initial length alonga longitudinal axis, and an outer electrode member that is concentricwith and surrounds the central electrode member, wherein the outerelectrode member includes a wall that is radially spaced from thecentral electrode member to define a gap between the wall and thecentral electrode member; transmitting a pulse of electric current alongthe central electrode member to generate a spark in the gap between thecentral electrode member and the outer electrode member, wherein thespark causes an air-fuel mixture to combust within the cylinder, thecentral electrode member to shorten from the initial length along thelongitudinal axis, and a concavity to develop in the wall of the outerelectrode member; and repeating the transmitting until the centralelectrode member has shortened from the initial length by at least 1.5millimeters to a reduced length.

In some implementations, a spark plug includes a housing defining alongitudinal axis, a first electrode having an electrode surfaceextending circumferentially around the longitudinal axis, and a secondelectrode including an electrode prong spaced from the electrode surfaceto form a spark gap between the first electrode and the secondelectrode. The electrode prong has a thickness t in a radial direction,a width w in a circumferential direction, and is spaced from theelectrode surface a gap length / of the spark gap in a radial direction.Further, t, w, and l together define a parameter P having a valueaccording to the equation

$P = \frac{w^{2}\sqrt{l_{1}}}{t^{2.5}}$

from approximately 1.5 to approximately 7.5.

In some implementations, a prechamber spark plug includes a housinghaving formed therein a combustion prechamber and a flow passage fromthe combustion prechamber. The spark plug further includes a firstelectrode, and a second electrode having a plurality of electrodeprongs. A plurality of spark gaps are defined between each one of theplurality of electrode prongs and the first electrode. Each of theplurality of electrode prongs has a thickness t and a width w and isspaced from the first electrode a gap length at a respective one of theplurality of spark gaps. Further, t, w, and l together define aparameter P according to the equation

$P = \frac{w^{2}\sqrt{l_{1}}}{t^{2.5}}$

having a value from approximately 1.5 to approximately 7.5.

In some implementations, a spark electrode assembly includes a firstelectrode having an electrode surface extending circumferentially arounda longitudinal axis, and a second electrode including an electrode prongsupported at a fixed location relative to the electrode surface. A sparkgap is formed between the electrode surface and the electrode prong. Theelectrode prong has a size defined by a thickness t and a width w, andis positioned at a gap length l of the spark gap from the electrodesurface that is based on a direct exponential relation to t and aninverse exponential relation tow, such that axial wear rates of theelectrode surface and the electrode prong are substantially equal.

In some implementations, a method of making a spark plug includesplacing a first electrode and a second electrode at a fixed position andorientation relative to one another, and forming, by way of the placinga first electrode and a second electrode, a spark gap between anelectrode surface of the first electrode extending circumferentiallyaround a longitudinal axis and an electrode prong of the secondelectrode. The method further includes establishing, by way of theforming a spark gap, a gap length of the spark gap in inverse relationto a width of the electrode prong, and in direct relation to a thicknessof the electrode prong.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of an example power system.

FIG. 2 is a side view of an example spark plug of the engine system.

FIG. 3 is a cross-sectional view of the spark plug in an initial state,taken along lines A- A of FIG. 2 .

FIG. 4 is a cross-sectional view of the spark plug in the initial state,taken along lines B- B of FIG. 2 .

FIG. 5 is a cross-sectional view of the spark plug in a final state,taken along lines A-A of FIG. 2 .

FIG. 6 is a cross-sectional view of the spark plug in the final state,taken along lines B-B of FIG. 2 .

FIG. 7 is a cross-sectional view of a part of a spark plug, according toanother embodiment.

FIG. 8 is another cross-sectional view of the spark plug as in FIG. 7 .

DETAILED DESCRIPTION

This disclosure relates to a spark plug, which is applicable tospark-ignition (SI) engines (e.g., a compressed natural gas(CNG)-powered engine, a methanol-powered engine, an ethanol-poweredengine, a bioethanol-powered engine, a gasoline-powered engine, agaseous hydrogen-powered engine, or another type of SI engine employingany of a variety of liquid fuels or gaseous fuels including blends)and/or systems including SI engines. Such engines and/or engine systemsmay be implemented in a machine, such as a generator, a movable machine(e.g., a motor vehicle, a railed vehicle, a watercraft, an aircraft), oranother type of machine.

To simplify the explanation below, the same reference numbers may beused to denote like features. The drawings may not be to scale.

FIG. 1 depicts a power system 100. The power system 100 includes an airinlet 102, a fuel tank 104, an ignition system 106, an engine 108, andan exhaust system 110. The air inlet 102 is a structure that isconfigured to receive and route air toward the engine 108. The fuel tank104 is a structure that is configured to receive and distribute fuel(e.g., CNG, methanol, ethanol, bioethanol, gasoline, or another type offuel) toward the engine 108 to mix with the air to form an air-fuelmixture. The ignition system 106 is a system that is configured toinitiate a combustion of the air-fuel mixture in the engine 108. Theignition system 106 includes an electrical energy source 112, such as anignition coil, that is electrically coupled to the engine 108. In someimplementations, the ignition system 106 may further include one or moreother electrical devices that are configured to control and/orcommunicate with the engine 108, such as an electronic control unit.

The engine 108 is a device that is configured to convert chemical energystored in the fuel into mechanical work (e.g., by driving a crankshaft).The engine 108 includes an engine block 114, at least one inlet valve116, a piston 118, a spark plug 120, and at least one outlet valve 122.The engine block 114, which includes at least one cylinder 124 and acylinder head 126, houses the inlet valve 116, the piston 118, the sparkplug 120, and the at least one outlet valve 122. The at least one inletvalve 116 is a mechanism that is configured to selectively permit theair-fuel mixture to enter the cylinder 124, which drives the piston 118downward toward a bottom dead center (BDC) position. The piston 118 is adevice that is movable within the cylinder 124 in a continuous cyclebetween the BDC position and a top dead center (TDC) position to propeland/or power a machine. During such movement, the piston 118 compressesthe air-fuel mixture. The spark plug 120, which is mounted to a bore 128within the cylinder head 126 above the cylinder 124, is a device that isconfigured to transmit an electric current from the electrical energysource 112 to cause the compressed air-fuel mixture to combust. A forceof the combustion drives the piston 118 back down toward the BDCposition. The at least one outlet valve 122 is a mechanism that isconfigured to selectively permit exhaust gas, resulting from combustion,to be expelled from the cylinder 124 as the piston 118 moves back to theTDC position.

The exhaust system 110 is a system, positioned downstream of the engine108, that is configured to reduce or remove emission compounds (e.g.,nitrous oxides (NOx), particulate matter, and/or hydrocarbons) from theexhaust gas to satisfy emission standards. For example, the exhaustsystem 110 may include a diesel particulate filter (DPF) (e.g., to treatthe particulate matter), a selective catalytic reduction (SCR) module(e.g., to treat the NOx), and/or a diesel oxidation catalyst (DOC)(e.g., to treat the hydrocarbons).

As indicated above, FIG. 1 is provided as an example. Other examples maydiffer from what is described with regard to FIG. 1 . For example, thenumber and arrangement of components (e.g., the air inlet 102, the fueltank 104, the ignition system 106, the engine 108, and/or the exhaustsystem 110) may differ from that shown in FIG. 1 . Thus, there may beadditional components, fewer components, different components,differently shaped components, differently sized components, and/ordifferently arranged components than those shown in FIG. 1 .

FIGS. 2-6 depict the spark plug 120. The spark plug 120 may include aprechamber spark plug as further discussed herein. As will also beexplained below, FIGS. 3-6 depict internal components of the spark plug120 in different states of wear. In particular, FIGS. 3-4 depict theinternal components of the spark plug 120 in an initial (e.g., unworn)state. FIGS. 5-6 depict the internal components of the spark plug 120 ina final (e.g., substantially worn) state.

The spark plug 120 includes a body 202 and a nozzle assembly 204 securedthereto. The body 202 includes an insulator 206 and a central conductor208. The insulator 206, which may be made of ceramic or another type ofelectrically-insulating material, is configured to electrically isolatethe central conductor 208 and maintain structural integrity of the sparkplug 120 in a high temperature environment. The insulator 206 includesan upper end surface 210, a lower end surface 302, and an exteriorsurface 212 that connects the upper end surface 210 to the lower endsurface 302. The upper end surface 210 includes an upper opening 214,and the lower end surface 302 includes a lower opening 304 thatcommunicates with the upper opening 214 to define a through hole 306.The exterior surface 212, which may be substantially cylindrical inshape, includes a plurality of annular ribs 216 and a flange 308. Theplurality of annular ribs 216 are arranged at a location proximate tothe upper end surface 210 and are configured to mitigate grounding ofthe electric current traveling through the spark plug 120. The flange308, which is arranged at a location proximate to the lower end surface302, is shaped and sized to facilitate attachment of the insulator 206to the nozzle assembly 204.

The central conductor 208 is a series of electrical conductors which aresequentially arranged along a longitudinal axis 218 of the spark plug120 and are together electrically connected to transmit the electriccurrent from the electric energy source 112 into the nozzle assembly204. The series of electrical conductors include a terminal connector220, a terminal pin 310, and a central electrode member 312. Theterminal connector 220 is a conductive component that is mounted to theupper end surface 210 of the insulator 206 and is configured to beconnected to a wire extending from the electrical energy source 112. Theterminal connector 220 may be, for example, made of a nickel alloy. Theterminal pin 310 is an elongated conductive element that is received inand extends along the through hole 306 of the insulator 206 to connectthe terminal connector 220 to the central electrode member 312. Theterminal pin 310 may be, for example, made of steel.

The central electrode member 312 is a conductive component that is sizedand arranged to interact with an outer electrode member 222 (describedbelow) to generate an electric arc or spark within the nozzle assembly204 to cause the air-fuel mixture to combust within the cylinder 124.The central electrode member 312, which may be made of a material suchas an iridium alloy or a platinum alloy, includes a central base 314 anda plurality of electrode prongs 316 extending therefrom. The centralbase 314 is secured within the through hole 306 and protrudes from thelower opening 301 of the insulator 206. As shown in FIG. 4 , the centralbase 314 is substantially centered on the longitudinal axis 218, whichextends through a geometric center of a first reference circle 402. Theplurality of electrode prongs 316, which may be substantially identicalto one another, may include six electrode prongs, five electrode prongs,four electrode prongs, or another quantity of electrode prongs. Otherarrangements of the plurality of electrode prongs 316 are contemplated.For example, the plurality of electrode prongs 316 may form anequiangular arrangement.

Each of the plurality of electrode prongs 316 (hereinafter referred toas the electrode prong 316) includes an axial portion 318 and a radialportion 320 that connects the axial portion 318 to the central base 314.The axial portion 318 extends in an axial direction and includes anouter surface 322 that defines a width w of the electrode prong 316 andpartially defines the first reference circle 402. In other words, theouter surfaces 322 of the axial portions 318 lie on the first referencecircle 402. The axial direction is substantially parallel to thelongitudinal axis 218. The radial portion 320 extends in a radialdirection that is substantially perpendicular to the longitudinal axis218. In some implementations, at least a portion of the radial portion320 may be curved and thus extend at an acute angle relative to theradial direction. As will be described below, the electrode prong 316 issized and positioned, relative to the nozzle assembly 204, in such a waythat extends a service life of the spark plug 120. For reference, theelectrode prong 316 further includes a thickness t that is substantiallyperpendicular to the width w.

The nozzle assembly 204 includes a housing 224, a gasket 226, and anouter electrode member 222. The housing 224, which may be made of carbonsteel, is configured to be secured to the exterior surface 212 of theinsulator 206. The housing 224 includes a first protruding segment 228,a second protruding segment 230, and a connection segment 232therebetween. The first protruding segment 228 includes a first uppersurface 234, a first lower surface 236, a first outer surface 238, and afirst inner surface 330. The first upper surface 234 is opposite to thefirst lower surface 236. The first outer surface 238, which is oppositeto the first inner surface 324, includes an engagement portion 240 thatis configured to be engaged by a tool or otherwise engaged to facilitateattachment of the spark plug 120 to the cylinder head 126. For example,the engagement portion 240 may include a hex protrusion that isconfigured to be rotated by a wrench. The first inner surface 324 isconfigured to be secured to the flange 308 of the insulator 206.

The second protruding segment 230 includes a second upper surface 242, asecond lower surface 244, a second outer surface 246, and a second innersurface 326. The second upper surface 242 faces the first lower surface236 and is opposite to the second lower surface 244. The second outersurface 246 includes external threads to facilitate threadably attachingthe spark plug 120 to the bore 128 within the cylinder head 126 toposition the outer electrode member 222 within the cylinder 124. Theconnection segment 232 is sized to improve sealing of the bore 128. Forexample, the connection segment 232 may have a relatively increasedlength in a range of approximately 5 millimeters (mm) to approximately 6mm.

The gasket 226 is an annular sealing component that is configured to besecured to the first lower surface 236 of the housing 224 to seal thebore 128 of the cylinder head 126. To resist creep, the gasket 226 maybe made of INCONEL® or a similar type of material. In other words, thegasket 226 may be configured to mitigate the potential of deformationdue to exposure to mechanical stresses associated with the combustionprocess.

The outer electrode member 222 is a conductive component that isconfigured to interact with the central electrode member 312 to generatethe electric arc therebetween. When attached to the housing 224 of thespark plug 120, as described below, the outer electrode member 222 isconcentric with and surrounds the central electrode member 312. Theouter electrode member 222, which may be made of a nickel alloy, aplatinum alloy, or an iridium alloy, includes a side wall 248 and abottom wall 250. The side wall 248 includes an exterior surface 252 andan interior surface 328 that is opposite to the exterior surface 252.The exterior surface 252 includes a first exterior axial portion 330, asecond exterior axial portion 254, and a radial portion 332 extendingtherebetween. The first exterior axial portion 330 is configured to beattached (e.g., via welding, soldering, and/or the like) to the secondinner surface 326 of the housing 224. The second exterior axial portion254, which has a diameter that is substantially equal to a diameter ofthe second outer surface 246 of the housing 224, includes a plurality ofexterior openings 256. The radial portion 332 is configured to beattached (e.g., via welding, soldering, and/or the like) to the secondlower surface 244 of the housing 224.

The interior surface 328 of the outer electrode member 222 is configuredto be radially spaced from the outer surfaces 322 of the axial portions318 of the plurality of electrode prongs 316. The interior surface 328includes a first interior axial portion 334 and a second interior axialportion 336, which may be substantially cylindrical in the initial stateof the spark plug 120. The first interior axial portion 334 is oppositeto the first exterior axial portion 330 of the side wall 248. The secondinterior axial portion 336, which is opposite to the second exterioraxial portion 332 and of side wall 248, includes a plurality of interioropenings 338 that fluidly communicate with the plurality of exterioropenings 256 to define a respective plurality of side wall flow passages258.

When the spark plus 120 is in the initial state, the interior surface328 of the outer electrode member 222 defines a second reference circle404. In other words, when the spark plug 120 is unworn, both the firstinterior axial portion 334 and the second interior axial portion 336 lieon the second reference circle 404. The second reference circle 404 hasa diameter that is greater than a diameter of the first reference circle402 by an initial length l₁ of a gap 340, across which the electriccurrent extends to form the electric arc.

The bottom wall 250 of the includes an upper surface 342, which has anupper opening 344, and a lower surface 260, which has a lower opening346. The lower opening 346 fluidly communicates with the upper opening344 to define a bottom wall flow passage 348. Together with theplurality of side wall flow passages 258, the bottom wall flow passage348 is configured to permit the air-fuel mixture to flow into acombustion prechamber or “pre-combustion chamber” 350 formed by acombination of the insulator 206, the housing 224, and the outerelectrode member 222.

As implemented within the power system 100, the spark plug 120 has alimited service life due to erosion of the central electrode member 312and the outer electrode member 222. Based on activating the power system100, the air-fuel mixture may flow into the pre- combustion chamber 350through the plurality of side wall flow passages 258 and the bottom wallflow passage 348 as the piston 118 travels upward toward the TDCposition to compress the air-fuel mixture. The electrical energy source112 transmits a pulse of electric current, which travels along thecentral conductor 208 and enters the pre-combustion chamber 350 as thepiston 118 approaches a desired position. Because the voltage of theelectric current exceeds a dielectric strength of the air-fuel mixture,the electric current bridges the gap 340 between the central electrodemember 312 and the outer electrode member 222. With the air-fuel mixtureionized by the electric current, a spark is generated to ignite anignition charge of fuel and air in the pre-combustion chamber 350 thattriggers ignition of a main charge of fuel and air within the cylinder124. As the engine 108 continues to operate, the spark plug 120 willcontinue to generate sparks between the central electrode member 312 andthe outer electrode member 222, which exposes the central electrodemember 312 and the outer electrode member 222 to extreme temperaturesand pressures within pre-combustion chamber 350. Due at least in part tosuch exposure, the plurality of electrode prongs 316 of the centralelectrode member 312 experience particle ejection and surface oxidation,which causes the plurality of electrode prongs 316 to gradually shortenalong the longitudinal axis 218 until reaching the final state shown inFIGS. 5-6 . At the same time, the first interior axial portion 334 ofthe interior surface 328 likewise experiences particle ejection andsurface oxidation, which causes a concavity 502 to develop in theinterior axial portion 334 and thus increases a length of the gap 340.As the plurality of electrode prongs 316 shorten, the concavity 502correspondingly elongates along the longitudinal axis 218 until likewisereaching the final state. When the spark plug 120 is in the final state,which marks an end of the service life of the spark plug 120, the pulsesof electric current are no longer able to bridge the gap 340, which hasincreased in size from the initial length l₁ (shown in FIGS. 3-4 ) to afinal length l₂ (as shown in FIGS. 5-6 ). In the final state, theplurality of electrode prongs 316 may have a reduced length that is lessthan an initial length of the plurality of electrode prongs 316 by atleast 1.5 mm.

In order to function as described above, the central electrode member312 and the outer electrode member 222 are sized and positioned relativeto one another such that a rate of shortening or “wear rate” of theplurality of electrode prongs 316 is substantially equal to a rate ofelongation of the concavity 502. In other words, based on the series ofelectric arcs extending through the air-fuel mixture within thepre-combustion chamber 350, the central electrode member 312 and theouter electrode member 222 are configured to wear at a substantiallyuniform rate along the longitudinal axis 218. To achieve thissubstantially uniform rate of wear, the central electrode member 312 andthe outer electrode member 222 are sized and arranged such that there isan inverse relationship between the width w of the electrode prong 316and the initial length l₁ of the gap 340. In some implementations, sucha relationship may be represented by the Equation 1:

$P = \frac{w^{2}\sqrt{l_{1}}}{t^{2.5}}$

where P is a parameter having a value in a range of approximately 1.5 toapproximately 7.5, w is the width of an electrode prong 316 in mm, l₁ isthe initial length of the gap 340 in mm, and t is the thickness of theelectrode prong 316 in mm. In some implementations, the value of theparameter P may be in a range of approximately 2.25 to approximately2.75. In some implementations, the value of the parameter P may be in arange of approximately 4.5 to approximately 5.5. Other values are hereincontemplated.

As indicated above, FIGS. 2-6 are provided as an example. Other examplesmay differ from what is described with regard to FIGS. 2-6 . Forexample, the number and arrangement of components may differ from thatshown in FIGS. 2-6 . Thus, there may be additional components, fewercomponents, different components, differently shaped components,differently sized components, and/or differently arranged componentsthan those shown in FIGS. 2-6 . For example, the outer electrode member222 may include a different arrangement and/or quantity of flow passages(e.g., one flow passage, two flow passages, or another quantity).

Turning now to FIGS. 7 and 8 , there are shown views of portions of aspark plug 420 according to one embodiment. The spark plug 420 hassimilarities to other embodiments described herein and, absentexplanation to the contrary, can be understood to function generallyanalogously to such other embodiments in an ignition system in aninternal combustion engine system. For instance, the components shown inFIGS. 7 and 8 are part of a spark plug including a nozzle assembly 424that could be swapped for some or all of a nozzle assembly as disclosedin connection with other embodiments. Moreover, except where otherwiseindicated or apparent from the context description and discussion hereinof any feature and/or functionality of any one embodiment can beunderstood to refer to features and/or functionality of any otherembodiment.

The spark plug 420 includes a housing 422 defining a longitudinal axis426. The housing 422 includes a tip piece 430 forming a pre-combustionchamber or combustion prechamber and one or more openings 434 from thecombustion prechamber 428 functionally analogous to openings describedelsewhere herein in connection with other embodiments. It will be notedthe openings 434 may be angularly oriented relative to the longitudinalaxis 426. The spark plug 420 might include a set of angularly orientedopenings 434 spaced circumferentially around the longitudinal axis 426and additionally or alternatively also include a centrally located endopening as depicted in the other embodiments and/or radially orientedopenings. The present disclosure contemplates at least one opening, andany number of openings in any suitable arrangement, to fluidly connect acombustion prechamber to a cylinder in an engine.

The spark plug 420 may include a nozzle assembly 424 formed by the tippiece 430, a housing body piece 436, and electrode components to bedescribed, again generally analogous to foregoing embodiments. A sparkelectrode assembly 438 is located in the housing 422 and includes afirst electrode 440 having an electrode surface 442 extendingcircumferentially around the longitudinal axis 426. The first electrode440 may include an inner electrode having a base 464 supported in aninsulator 468 in some embodiments. The first electrode 440 extends intothe prechamber 428 to a terminal electrode tip 462. As illustrated, thefirst electrode 440 may be centrally located in the spark plug 420 andgenerally extends axially along the longitudinal axis 426. Embodimentswhere an inner electrode is offset in a radial direction from alongitudinal axis defined by a spark plug housing would neverthelessfall within the scope of the present disclosure.

The spark electrode assembly 438 further includes a second electrode444. Second electrode 444 may be electrically connected to the housing422, such as by direct physical attachment or unattached but directphysical and electrical contact with tip piece 430. The second electrode444 may be one of a plurality of second electrodes each including anelectrode prong 446. The electrode prongs 446 may be spacedcircumferentially around the longitudinal axis 426. The electrode prongs446 may also be understood as spaced circumferentially around the firstelectrode 440 and the electrode surface 442. The electrode prongs 446may be substantially identical to one another, and thus description anddiscussion herein of a second electrode or an electrode prong in thesingular will be understood by way of analogy to refer to any of aplurality of second electrodes and/or electrode prongs.

The electrode prong 446 is spaced from the electrode surface 442 to forma spark gap 448 between the first electrode 440 and the second electrode444. It will be appreciated a plurality of spark gaps are formed betweenthe first electrode 440 and the second electrode 444/ electrode prongs446. In an embodiment, a number of the electrode prongs 446 is 4 orgreater. In some implementations, a number of the electrode prongs 446is 5 or greater, and potentially 6 or greater as in the depiction ofFIGS. 7 and 8 where a total of 8 electrode prongs of the secondelectrode 444 are provided.

It will be appreciated that in the embodiment of FIGS. 7 and 8 thesecond electrode 444 includes an outer electrode that is radiallyoutward of the first electrode 440. The tip piece 430 includes an innersurface 431 forming the prechamber 428 and extending circumferentiallyaround the longitudinal axis 426 at a location radially outward of thefirst electrode 440 and the second electrode 444. The inner surface 431may extend continuously circumferentially around the longitudinal axis426. The electrode surface 442 may likewise extend continuouslycircumferentially around the longitudinal axis 426. The electrode prong446 may also include a radial portion 454 extending radially inward fromthe tip piece 430 in a direction of the first electrode 440 andgenerally along a radius of a circle defined by the longitudinal axis426. The electrode prong 446 may also include an axial portion 456extending generally along the electrode surface 442 in an axialdirection. A bend section 458 of the electrode prong 446 connectsbetween the radial portion 454 and the axial portion 456. The axialportion 456 is radially inward of the radial portion 454 and extends toa terminal end or electrode tip 452. The electrode tip 452 may be spacedan offset distance 460 in an axial direction from the tip 462 of thefirst electrode 440. Put differently, the first electrode 440 may extendin an axially outward direction along the longitudinal axis 426 agreater distance than does the electrode prong 446.

As noted above, the spark plug 420 has similarities to the otherembodiments discussed herein. It will be recalled the central electrodein the embodiments of FIGS. 2-6 includes electrode prongs that formspark gaps together with an electrode surface of an outer electrodemember. In the case of the embodiment of FIGS. 7 and 8 , the first,inner electrode 440 is surrounded by the electrode prongs 446 of thesecond, outer electrode 444. The geometry of the electrode prongs 446may nevertheless be similar or substantially identical in certainrespects to that of the electrode prongs of the spark plug 120.

The electrode prong 446 has a thickness tin a radial direction, a widthw in a circumferential direction, and is spaced from the electrodesurface 442 a gap length l₁ of the spark gap 448 in the radialdirection. Moreover, t, w, and l₁ together define a parameter P having avalue from approximately 1.5 to approximately 7.5 according to Equation1 set forth above. In some implementations, P has a value fromapproximately 4.5 to approximately 5.5. In other implementations, P hasa value from approximately 2.25 to approximately 2.75. The value of Pmay thus be from approximately 2.25 to approximately 5.5 in someembodiments, and having a value in a range having as a lower limitapproximately 2.5 and/or having as an upper limit approximately 5.5. Insome implementations w is greater than or equal to t. The electrodeprong 446 may have a substantially uniform width and substantiallyuniform thickness throughout, and typically at least within axialportion 456.

The spark plug 420 can be operated with either of a first polarity or asecond polarity. In one implementation the first electrode 440 is acathode and the second electrode 440 is an anode, with the electricalenergy source 112 structured to energize a spark control circuit suchthat charge flows from the first electrode 440 to the second electrode440. In other implementations, the electrical energy source 112 isstructured to energize a spark control circuit such that charge flowsfrom the electrode prongs 446 of the second electrode 440 to theelectrode surface 442 of the first electrode 440 with the firstelectrode 440 being the anode and the second electrode 440 being thecathode. The latter implementation can be associated with furtherextended service life as compared to certain known strategies.

According to the present disclosure, and as will be appreciated from theabove Equation 1, the electrode prong 446 has a size defined by thethickness t and the width w, and is positioned at the gap length l₁ ofthe spark gap 448 from the electrode surface 442 that is based on adirect exponential relation to t and an inverse exponential relation tow, such that axial wear rates of the electrode surface 442 and theelectrode prong 446 are substantially equal. Principles of the equalwear rates as applicable to all embodiments of the present disclosureare further discussed herein.

INDUSTRIAL APPLICABILITY

Referring to the drawings and various embodiments generally, but byexemplary reference to FIGS. 2-6 , the spark plug 120 of the presentdisclosure is particularly applicable within the engine 108 of the powersystem 100. The engine 108 may be configured to utilize fuel (e.g., CNG,methanol, ethanol, bioethanol, gasoline, and/or the like) to power agenerator, propel a movable machine (e.g., a motor vehicle, a railedvehicle, a watercraft, an aircraft), and/or the like. In contrast tospark plugs of the prior art, in which electrodes tend to wear unevenlyand thus waste material that might otherwise have been utilized togenerate additional sparks, the spark plug 120 of the present disclosureis configured such that the central electrode member 312 wears along thelongitudinal axis 218 at a rate that is substantially equal to that ofthe outer electrode member 222. As a result, the spark plug 120 has anextended service life compared to spark plugs of the prior art, with thecentral electrode member 312 being configured to shorten by at least 1.5mm along the longitudinal axis 218 from an initial length to a reducedlength. Furthermore, due to the narrower and/or thinner design of theplurality of electrode prongs 316, more space is available within thepre-combustion chamber 350. As a result, the central electrode member312 may include additional electrode prongs 316 which are thus capableof further extending the service life of the spark plug 120. Because thespark plug 120 has an increased service life relative to other sparkplugs, the spark plug 120, when utilized within the power system 100,may conserve material and expenses that would otherwise result fromrepair and/or replacement of the spark plug 120.

The normalization of the wear rates between a first electrode and asecond electrode according to the present disclosure produce a materialerosion phenomenon that can be understood as a “wicking” progression ofwear. The wicking progression of wear proceeds akin to burning of acandle to displace material from an electrode prong in a predictable andrelatively uniform manner that better matches a wear rate of theassociated other electrode. As a result, neither electrode outpaces theother and a greater amount of the electrode prong can be consumed beforea gap distance becomes too large to be practicably bridged. The presentdisclosure also reflects the insight that a material area of anelectrode prong and a length of separation (the gap length l₁) can beoptimized to promote the normalization of wear rate between therespective electrodes. Whereas as discussed above earlier spark plug andspark electrode assemblies were often observed to wear away only arelatively small portion of a precious metal electrode prong, of iridiumor platinum for example, before the spark plug would fail, according tothe present disclosure a majority and in some instances nearly anentirety of an axial portion of an electrode prong can be consumedduring service. Also differing from prior art spark plugs and sparkelectrode assemblies generally, according to the present disclosure thegap length l₁ may be established in inverse exponential relation to theelectrode prong width w and in direct exponential relation to theelectrode prong thickness t as discussed above. Conventional practicescommonly establish a larger spark gap length where more electrodematerial is present, and a shorter spark gap length where less materialis present. Thus, the present disclosure also proceeds counter tocertain conventional practices in exploiting the discovery that arelatively narrower electrode prong may be advantageously positioned forextended service life relatively further from a second electrode ratherthan relatively closer.

Making spark plugs according to the present disclosure can includeplacing a first electrode and a second electrode at a fixed position andorientation relative to one another. In the case of the embodiment ofFIGS. 7 and 8 , this step could include installing the tip piece 430 inor on the housing piece 436. The first electrode 440 may be supported ininsulator 468 which is in turn supported in housing piece 436. Thesecond electrode 446 may be attached to tip piece 430 and secured tohousing piece 436 to thus support the first electrode 440 and the secondelectrode 446 at the fixed position and orientation.

Making a spark plug according to the present disclosure can furtherinclude forming, by way of the placing a first electrode and a secondelectrode, a spark gap between an electrode surface of the firstelectrode extending circumferentially around a longitudinal axis and anelectrode prong of the second electrode. In the case of the embodimentof FIGS. 7 and 8 this step could be part of the final positioning andattachment of the tip piece 430 to the housing piece 436. By way of theforming of a spark gap, a gap length of the spark gap is establishedthat is in inverse relation to a width of the electrode prong, and indirect relation to a thickness of the electrode prong. As discussedabove, the inverse relation may be an exponential relation and thedirect relation may be an exponential relation. Establishing a gaplength may include setting the gap length in direct relation to aparameter P as defined in the above Equation 1 having a value fromapproximately 1.5 to approximately 7.5. Making a spark plug can alsoinclude as part of the steps discussed above, or separately depending onspark plug design, positioning a spark gap of a spark electrode assemblywithin a combustion prechamber.

The foregoing disclosure provides illustration and description, but isnot intended to be exhaustive or to limit the implementations to theprecise forms disclosed. Modifications and variations may be made inlight of the above disclosure or may be acquired from practice of theimplementations. Furthermore, any of the implementations describedherein may be combined unless the foregoing disclosure expresslyprovides a reason that one or more implementations cannot be combined.Even though particular combinations of features are recited in theclaims and/or disclosed in the specification, these combinations are notintended to limit the disclosure of various implementations. Althougheach dependent claim listed below may directly depend on only one claim,the disclosure of various implementations includes each dependent claimin combination with every other claim in the claim set.

As used herein, “a,” “an,” and a “set” are intended to include one ormore items, and may be used interchangeably with “one or more.” Further,as used herein, the article “the” is intended to include one or moreitems referenced in connection with the article “the” and may be usedinterchangeably with “the one or more.” Further, as used herein, theterms “comprises,” “comprising,” “having,” “including,” or othervariations thereof, are intended to cover non- exclusion, such that aprocess, method, article, or apparatus that comprises a list of elementsdoes not include only those elements, but may include other elements notexpressly listed. In addition, in this disclosure, relative terms, suchas, for example, “about,” “generally,” “substantially,” and“approximately” are used to indicate a possible variation of ±10% of thestated value, except where otherwise apparent to one of ordinary skillin the art from the context. Further, the phrase “based on” is intendedto mean “based, at least in part, on” unless explicitly statedotherwise. Also, as used herein, the term “or” is intended to beinclusive when used in a series and may be used interchangeably with“and/or,” unless explicitly stated otherwise (e.g., if used incombination with “either” or “only one of”). Further, spatially relativeterms, such as “below,” “lower,” “above,” “upper,” and the like, may beused herein for ease of description to describe one element or feature'srelationship to another element(s) or feature(s) as illustrated in thefigures. The spatially relative terms are intended to encompassdifferent orientations of the apparatus, device, and/or element in useor operation in addition to the orientation depicted in the figures. Theapparatus may be otherwise oriented (rotated 90 degrees or at otherorientations) and the spatially relative descriptors used herein maylikewise be interpreted accordingly.

What is claimed is:
 1. A spark plug comprising: a housing defining alongitudinal axis; a first electrode having an electrode surfaceextending circumferentially around the longitudinal axis; a secondelectrode including an electrode prong spaced from the electrode surfaceto form a spark gap between the first electrode and the secondelectrode; the electrode prong having a thickness (t) in a radialdirection, a width (w) in a circumferential direction, and spaced fromthe electrode surface a gap length (l₁) of the spark gap in the radialdirection; and t, w, and l together define a parameter P having a valueaccording to the equation $P = \frac{w^{2}\sqrt{l}}{t^{2.5}}$ fromapproximately 1.5 to approximately 7.5.
 2. The spark plug of claim 1wherein the electrode surface extends continuously circumferentiallyaround the longitudinal axis.
 3. The spark plug of claim 1 wherein thehousing forms a combustion prechamber, and the spark gap is within thecombustion prechamber.
 4. The spark plug of claim 3 wherein theelectrode prong is one of a plurality of electrode prongs spacedcircumferentially around the longitudinal axis.
 5. The spark plug ofclaim 4 wherein the first electrode includes an outer electrode radiallyoutward of the second electrode.
 6. The spark plug of claim 4 whereinthe first electrode includes an inner electrode radially inward of thesecond electrode, and the plurality of electrode prongs are spacedcircumferentially around the first electrode.
 7. The spark plug of claim6 wherein each of the plurality of electrode prongs includes a radialportion extending radially inward in a direction of the first electrode,and an axial portion extending from a respective one of the radialportions in an axial direction along the first electrode to an electrodetip.
 8. The spark plug of claim 1 wherein P has a value fromapproximately 4.5 to approximately 5.5.
 9. The spark plug of claim 1wherein P has a value from approximately 2.25 to 2.75.
 10. A prechamberspark plug comprising: a housing having formed therein a combustionprechamber and a flow passage from the combustion prechamber; a firstelectrode; a second electrode including a plurality of electrode prongs;a plurality of spark gaps defined between the plurality of electrodeprongs and the first electrode; each of the plurality of electrodeprongs having a thickness (t) and a width (w), and being spaced from thefirst electrode a gap length (l₁) at a respective one of the pluralityof spark gaps; and t, w, and l₁ together define a parameter P accordingto the equation $P = \frac{w^{2}\sqrt{l}}{t^{2.5}}$ having a value fromapproximately 1.5 to approximately 7.5.
 11. The spark plug of claim 10wherein P is in a range having as a lower limit approximately 2.5 orhaving as an upper limit approximately 5.5.
 12. The spark plug of claim10 wherein w is greater than or equal to t.
 13. The spark plug of claim10 wherein the first electrode includes an outer electrode.
 14. Thespark plug of claim 13 wherein the housing defines a longitudinal axis,and the second electrode is centered on the longitudinal axis andprojects into the combustion prechamber; and each of the plurality ofelectrode prongs includes a radial portion extending radially outward ina direction of the first electrode, and an axial portion extending froma respective one of the radial portions in an axial direction along thefirst electrode.
 15. The spark plug of claim 10 wherein the firstelectrode includes an inner electrode, and the plurality of electrodeprongs are spaced circumferentially around the first electrode andelectrically connected to the housing.
 16. The spark plug of claim 15wherein: the housing defines a longitudinal axis, and the firstelectrode is located on the longitudinal axis and projects into thecombustion prechamber; and each of the plurality of electrode prongsincludes a radial portion extending radially inward from the housing ina direction of the first electrode, and an axial portion extending froma respective one of the radial portions in an axial direction along thefirst electrode.
 17. An ignition system comprising the spark plug ofclaim 15 and an electrical energy source configured to energize thefirst electrode as a cathode and the second electrode as an anode.
 18. Aspark electrode assembly comprising: a first electrode including anelectrode surface extending circumferentially around a longitudinalaxis; a second electrode including an electrode prong supported at afixed location relative to the electrode surface; a spark gap is formedbetween the electrode surface and the electrode prong; and the electrodeprong has a size defined by a thickness (t) and a width (w), and ispositioned at a gap length (l₁) of the spark gap from the electrodesurface that is based on a direct exponential relation to t and aninverse exponential relation to w, such that axial wear rates of theelectrode surface and the electrode prong are substantially equal. 19.The spark electrode assembly of claim 18 wherein h is defined by thedirect exponential relation to t, the inverse exponential relation to w,and a direct relation to a parameter P having a value from approximately1.5 to approximately 7.5.
 20. The spark electrode assembly of claim 19wherein P is in a range having as a lower limit approximately 2.5 orhaving as an upper limit approximately 5.5.
 21. The spark electrodeassembly of claim 18 wherein the electrode prong includes a radialportion and an axial portion, and wherein w is greater than or equal tot, and w and t are substantially uniform within the axial portion. 22.The spark electrode assembly of claim 18 wherein the first electrodeincludes an outer electrode, and the electrode prong is one of aplurality of electrode prongs spaced circumferentially around thelongitudinal axis.
 23. The spark electrode assembly of claim 20 furthercomprising a housing, and wherein the first electrode includes a centralelectrode within the housing, and the electrode prong is one of aplurality of electrode prongs spaced circumferentially around thecentral electrode and electrically connected to the housing.
 24. Amethod of making a spark plug comprising: placing a first electrode anda second electrode at a fixed position and orientation relative to oneanother; forming, by way of the placing a first electrode and a secondelectrode, a spark gap between an electrode surface of the firstelectrode extending circumferentially around a longitudinal axis and anelectrode prong of the second electrode; and establishing, by way of theforming a spark gap, a gap length of the spark gap in inverse relationto a width of the electrode prong, and in direct relation to a thicknessof the electrode prong.
 25. The method of claim 24 wherein theestablishing a gap length includes setting the gap length in directrelation to a parameter P having a value from approximately 1.5 toapproximately 7.5.
 26. The method of claim 25 wherein the establishing agap length includes establishing the gap length (l₁) based on the width(w) of the electrode prong and the thickness (t) of the electrode prong,such that t, w, l₁, and P having values according to the equation$P = \frac{w^{2}\sqrt{l}}{t^{2.5}}$
 27. The method of claim 24 furthercomprising locating the spark gap within a combustion prechamber in anozzle assembly; wherein the electrode prong is one of a plurality ofelectrode prongs of the second electrode, and the placing the firstelectrode and the second electrode further includes placing the firstelectrode radially outward of the second electrode.